我有一台 CentOS 7.8 服务器，它使用 PTP4L PTP 服务同步时钟。我希望该服务在无法与外部服务器同步时失败，因此我使用--gmCapable=0.不过，这似乎没有影响。当它无法到达外部时间服务器时，它只会使用本地时钟作为大师，给人一种一切正常的错误印象。我怎样才能防止这种情况发生？
# service ptp4l status
Redirecting to /bin/systemctl status ptp4l.service
● ptp4l.service - Precision Time Protocol (PTP) service
Loaded: loaded (/usr/lib/systemd/system/ptp4l.service; enabled; vendor preset: disabled)
Active: active (running) since Tue 2020-05-12 15:38:33 CEST; 13s ago
Main PID: 48280 (ptp4l)
CGroup: /system.slice/ptp4l.service
└─48280 /usr/sbin/ptp4l -f /etc/ptp4l.conf -i enp65s0f1 --gmCapable=0
May 12 15:38:33 eurex-tr5.veloquant.com systemd[1]: Started Precision Time Protocol (PTP) service.
May 12 15:38:33 eurex-tr5.veloquant.com ptp4l[48280]: [149997.679] selected /dev/ptp1 as PTP clock
May 12 15:38:33 eurex-tr5.veloquant.com ptp4l[48280]: [149997.681] port 1: INITIALIZING to LISTENING on INIT_COMPLETE
May 12 15:38:33 eurex-tr5.veloquant.com ptp4l[48280]: [149997.681] port 0: INITIALIZING to LISTENING on INIT_COMPLETE
May 12 15:38:40 eurex-tr5.veloquant.com ptp4l[48280]: [150004.734] port 1: LISTENING to MASTER on ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES
May 12 15:38:40 eurex-tr5.veloquant.com ptp4l[48280]: [150004.734] selected local clock 3cecef.fffe.015d03 as best master
May 12 15:38:40 eurex-tr5.veloquant.com ptp4l[48280]: [150004.734] assuming the grand master role